We took a co-worker’s monitor power cable and ran it through the wall into a separate power strip/surge protector so we could turn his monitor on/off at our leisure.

Taping up the microphone of someone’s phone, causing them to speak louder.

Put a piece of clear tape on the glass of the photocopier. This is fun, but it has a second part to it. If the sheer frustration of someone having to make 100 copies all over again isn’t enough, you could try making 100 copies of the piece of tape, and then load the paper into the paper feed. Funny to see people go crazy trying to figure out why the copy is coming up with this square on every page.

Post a For Sale on the lunchroom posterboard with your co-workers extension, offering to sell “One size adult XL outfit of baby clothing, including pacifier, bottle, bib and diaper.”